The present invention relates to apparatus for determining the point or points at which drill pipe, casing or tubing is stuck in a borehole traversing earth formations. Primarily, this apparatus detects the stuck point above which the pipe may be removed.
The approximate location of the stuck point may be estimated from the surface by stretching the free pipe above the stuck point. Then, a stuck point indicating device is lowered into the pipe to locate the actual stuck point. The stuck point indicating device generally consists of a pair of spaced members connected by a sensing means that permits a limited amount of relative movement between the spaced members and produces a signal representing the relative movement between the members when the drill pipe is stretched from the surface.
In a stuck point measurement each spaced member is temporarily connected to the pipe and a force applied to the upper portion of the pipe. The force may be upward, downward or rotational. When, for example, a force in the form of torque is applied to the upper end of the pipe to twist the pipe, the length of the pipe above the stuck point will twist as indicated by relative movement between the spaced members whereas the pipe below the stuck point will not. The device is progressively lowered down through the pipe, applying a twist to the pipe after the device is positioned in the pipe until the device passes the stuck point, at which point no relative rotation of the individual spaced members will occur.
After the stuck point is located, the free pipe above the stuck point may be removed from the well by conventional methods.